Factory and processing plant environments are so diverse that they are difficult to describe in specific terms. Many difficulties are encountered in trying to understand plant operation in a general way because of this diversity. There do exist, however, in the field of manufacturing, some common operational characteristics that a factory or processing plant should possess for efficiency purposes. In particular, it has become increasingly desirable for a plant to be operated in an optimal manner with respect to material resources, human resources and time. Areas of focus, in this regard, include the utilization of sound engineering principals, economic planning and safety.
Simulation modules of plant operation, which incorporate specific knowledge of plant operation, aid in implementing such principals in practice. Because of the complexity of most plant environments, however, experts such as manufacturing engineers only have knowledge limited to the particular areas of the plant domain within which they work. This knowledge may exist in different forms ranging from analytical models to heuristics. Because of the incompatibility of the forms of knowledge, it is very difficult to incorporate the knowledge in a complete plant model.
The application of computer technology in the plant environment is commonplace. In all areas of production, one can find computers used for a variety of tasks from control of equipment to data logging. One particular area that is growing is the use of computers to implement knowledge-based systems, or expert systems, in the plant domain to aid in achieving plant operation efficiency. A knowledge-based system contains a representation of knowledge about some aspect of the plant operation, and it provides diagnoses or recommendations by using some form of logical reasoning or heuristics to process the knowledge. The systems represent a distinct use of computers beyond numerically-based applications. Attempts have been made to create a knowledge-based system with which one can combine the power of the computer with the expertise of plant operators to yield a tool that can assist in the operation of the plant, and provide diagnostic information that can be used to monitor the plant and its resources. Because a plant may have many different knowledge sources and expert systems, a method of integration would allow interaction among different systems and would permit broader issues of plant operation to be incorporated within the computation framework. Because of the different forms of knowledge sources and expert systems, such a method of integration has not been achieved to model complete plant operation. In addition, because every plant differs somewhat in specific areas, a system has not been realized which possesses functional modules in an overall structure sufficiently broad to be useful in diverse plant environments.
In order to achieve such a system, it is important to model characteristics of every plant that are common. One such characteristic common to every plant is that in some complex way, inputs (raw materials) are processed to produce outputs (finished products). Another common aspect is that all plants involve processing over time. Unfortunately, a complete analytical description of a plant involving full time dependencies is impractical, if not impossible. Information concerning a plant operation is typically incomplete and fragmentary. Abundant information relating to plant operation, however, may exist, but in order to create a system, it must be gathered and organized into such a system. This has not been done successfully in the past with knowledge-based systems.
Accordingly, a general object of the present invention is to provide a knowledge-based system which possesses functional modules in an overall structure sufficiently broad to be useful in diverse plant environments.
Another object of the present invention is to provide a knowledge-based system which can combine the power of the computer with expertise of plant operators to yield a tool that can provide diagnostic information and monitor operation of the plant.
Another object of the present invention is to provide a case-based knowledge source process in which a comparison scheme provides for comparisons in both a time and magnitude fashion.